High-speed connector with multi-stage compensation

ABSTRACT

A communication connector uses compensation circuitry to compensate for crosstalk in a network connection. Portions of the compensation circuitry are placed on a flexible circuit board that makes conductive contact with plug interface contacts of the connector. Additional compensation circuitry is provided on a rigid circuit board within the connector.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/090,403, filed Aug. 20, 2008, the subject matter of which ishereby incorporated by reference in its entirety.

BACKGROUND

There is a need to improve near-end crosstalk (NEXT), far-end crosstalk(FEXT) and return loss performance of communications connectors athigher frequencies in a robust design that can be relatively easilymanufactured. This description is directed to a method of improving theperformance of a communication connector by employing specificcapacitive and inductive couplings on a printed circuit board (PCB)within the connector.

DESCRIPTION OF THE INVENTION

An improved electrical communication jack having improved NEXT, FEXT,and return loss performance is shown and described. Additionally, thisjack reduces the differential-to-common and common-to-differential modeconversion (herein referred to as “mode conversion”) that occurs withinthe jack to improve the alien crosstalk performance of the system.

The printed circuit board (PCB) designs described herein may be employedin an EIA/TIA CAT6A modular jack assembly, which includes a two-stagecapacitor compensation/crosstalk with time delay, employs a version of alattice network as described further below, and exhibits improved modeconversion properties. In some embodiments, a flex board 24 and rigidboard 16, as shown in FIG. 1, work together to provide the desiredperformance characteristics of the jack.

Time delay compensation in an electrical connector achieves improvedtransmission performance for near-end crosstalk by introducingpredetermined amounts of compensation and crosstalk between two pairs ofconductors that extend from the connector's input terminals to itsoutput terminals along interconnection paths. Electrical signals on onepair of conductors are coupled onto the other pair of conductors in twoor more compensation stages that are time delayed with respect to eachother. Generally, in a first stage the compensating crosstalk nearer tothe plug is of an opposite magnitude of the net crosstalk caused by theplug. The second stage of crosstalk is generally of the same polarity asthe net crosstalk caused by the plug, and is placed further away fromthe plug than the first stage. The differing time delays between thestages cause the phases of these stages to change at different rateswith increasing frequency. This then creates a specific frequency whereall of the stages add together to essentially cancel out and create anull, which in turn increases the overall NEXT bandwidth of the matedplug and jack.

According to one embodiment of the present invention, a CAT6A RJ45 jack10 has a housing 12 that fits an RJ45 plug, a nose 14 that has eightplug interface contacts (PICs) that mate with a plug and interface witha rigid board 16, where the rigid board 16 connects to insulationdisplacement contacts (IDCs) 18, a rear sled 20 that holds the IDCs, anda wire cap 22 that allows for wires within cabling (not shown) toconnect with the IDCs. The nose 14 also includes a flex circuit board24, plug interface contacts 26, front bottom sled 28 and front top sled30. Both the flex circuit board 24 and rigid circuit board 16 containcircuitry designed to improve NEXT, FEXT, return loss, and modeconversion properties of the jack.

CAT6A products generally have eight wires that make up four differentialpairs. These wires are numbered numerically 1 through 8, and thedifferential pairs are 45, 36, 12, and 78 (pairs 1, 2, 3, and 4,respectively). The layout of these wires within an RJ45 plug causescrosstalk between these differential pairs that must be compensated forwithin a jack. Since there are four differential pairs, near endcrosstalk (NEXT) can form between the six different pair combinations.These pair combinations are 45-36, 45-12, 45-78, 36-12, 36-78, and12-78. In different embodiments of the present invention, compensationis achieved by positioning traces on circuit boards within a jack.

Self-inductive stubs as used herein (shown in FIGS. 2, 6-8, and 13-15)refer to circuit board traces that are made specific lengths to create aself-inductance of a given value. The term “stub” refers to the factthat these traces are not part of the main current carrying path. Theyare stubs off of the current carrying path, and end in a capacitor(having no DC connections at their ends). Current carrying paths aretraces that allow a DC current to flow between two points (such as theRJ45 plug and the insulation displacement contacts 16 (IDCs) in thejack).

A lattice network as described herein generally includes a crosstalkcircuit component and a compensation circuit component each of which hasa different coupling rate versus frequency. A “crosstalk circuitcomponent” is a circuit component in which coupling occurs with the samepolarity as the crosstalk-producing coupling within a plug, while a“compensation circuit component” is a circuit component in whichcoupling occurs at a polarity that is opposite the polarity of thecrosstalk coupling that occurs within a plug.

The version of the lattice network used in this invention adds a secondself-inductive stub connected between a capacitor and the second signaltrace to the 2nd stage crosstalk network. Previous designs have employedwhat could be called an “LC” circuit, having most of the inductanceattached to one end of the capacitor. The design of one embodiment ofthe current invention could be termed an “LCL” circuit, having theinductor split such that significant inductances are used on both sidesof the capacitor.

Self-inductive stubs, as described herein, use the distributedelectrical parameter of inductance per unit length of the circuit traceto produce inductive elements. Although this is modeled in theschematics as a discrete inductor (which is appropriate as it has anequivalent effect) it is a distributed inductive component produced bythe length of the traces as opposed to turns of a wire coil, forexample. In contrast, the capacitors shown herein are discretecapacitors although both the capacitors and the inductors shown can berealized by discrete or distributed components, or as a combinationthereof.

Positioning a capacitor between two stubs improves NEXT performance,relative to the opposite transmission direction (IDC to PIC), comparedto putting a single inductor on only one side of that capacitor, wherethe inductance of the single inductor, L1, is about equal to L2+L3 asshown in FIG. 2. Additionally, the second stub shows improvement inreturn loss, also relative to using only a “one-sided” inductor.

The self inductive stubs, along with corresponding capacitors (forexample, the L5-C56-L6 combination and L3-C34-L4 combination as shown inFIG. 6), may be modeled as an LC circuit with a resonance effect havinga resonant frequency of f_(o)=1/(2π√LC). The selection of the inductanceand capacitance values (i.e., the Ls and the Cs) is generally anonlinear multivariable optimization with multiple objective functions,(the “objective functions” being improved NEXT, FEXT, return loss,etc.). Consequently, selection of a given L or C value is not madeindependent of other circuit considerations. Some of the considerationsfor selecting a given L value include: if it is too low the resonancepoint moves to a higher frequency and there is no desired NEXTimprovement in the signal frequency operation range of interest; if theinductance is too high: a) the inductive traces become too long to fiton a typical rigid board; b) the resonance can move into the frequencyoperation range of interest, possibly introducing deleterious effects;and c) there can be a degradation of return loss.

The general design of a CAT 6A jack according to one embodiment of thepresent invention uses a two-stage capacitor compensation/crosstalk withtime delay for pair combinations 45-36, 36-12, 36-78, and 45-12. Theflex board 24 contains the first stage capacitors in the time delaymodel for pair combinations 45-36, 36-12, and 36-78 (the flex boardincludes capacitors C35, C45, C26, and C37). The rigid board 16 thencontains the second stage capacitors in the time delay model forspecific pair combinations (C46, C56, C16, and C38). The combination ofa flex board 24 and a rigid board 16 for pair combination 45-36 alsoincludes a lattice network which additionally uses self-inductors L3,L4, L5, and L6 and the additional capacitors C35 and C46 on the rigidboard 16 (there is no lattice network on any other pairs for thisembodiment).

This description takes into account the following:

-   -   All capacitor dimensions given are referenced relative to the        amount of overlap occurring between the pads. One conductive        layer of each capacitor is oversized 10 mils to help account for        layer-to-layer registration. The dimensions given are for the        smaller layer. According to one embodiment, rigid board        capacitors are formed across a 4 mil core, generally made of an        FR4 material having a dielectric constant of approximately 4.4.        Flex board capacitors are formed across a 1 mil core, generally        made of a material having a dielectric constant of approximately        3.4.    -   The schematics shown for each description include only the        intentional capacitance added by design. For example, mutual        inductance between wires is purposely not shown for schematic        clarity and due to the fact that any mutual inductance that        results from the design is not intentionally used for        compensation.    -   These schematics do not show parasitic capacitances caused by        the geometry of the setup unless this parasitic capacitance is        deemed important to note (values greater than 0.1 pF). These        values are noted, but not labeled with reference characters.    -   The schematics shown for each pair combination (FIGS. 9-13) do        not show all connections since they are only showing two pairs        at once. A full schematic of the rigid board 16 can be seen in        FIG. 6.    -   The distance causing a time delay from the flex board to the PIC        interface on the rigid board is approximated as 0.5″ for all        pair combinations.    -   The schematics shown attempt to approximate a “middle plug”        which by definition per the EIA/TIA CAT6A standards refers to a        plug whose crosstalk value is in the middle of the range of        crosstalk values specified for that pair combination.    -   All circuit board dimensions described herein are each        individually subject to change (estimates up to 20%). One reason        for this is variability of circuit board build tolerances from        different circuit board manufacturers. Different materials or        different processes may be used to manufacture the circuit        boards. Therefore, the performance of the circuit board may        change even though the artwork is identical due to the        capacitance changing. Another reason is to allow for design        changes required to compensate the many different jack designs        (for example, modular jacks, shielded jacks, and unshielded        jacks). Consequently, good engineering practice requires the        ability to change the area of overlap for the pad capacitors by        the specification tolerance (±20%). This change in area may be        done on a capacitor-by-capacitor basis, and the overall board        design (trace layout, use of time delay, lattice) remains        identical. Some variants may only require changing the size of        one or two capacitors (either smaller or larger), and some may        require changing the sizes of all capacitors.    -   The jack designs described herein can be used for several types        of products, among them shielded, unshielded, and punchdown-type        connectors. Further, the jack housing 12 or another component of        the jack may be covered with a conductive foil to reduce alien        crosstalk effects.

Flex Circuit Board

The flex circuit board 24 shown in FIG. 1 is described in more detail inFIGS. 3-5. FIG. 3 shows a schematic diagram of the flex circuit board,FIG. 4 shows the traces provided on two conductive layers of the flexcircuit board, and FIG. 5 is a perspective view of the flex circuitboard in which both layers of conductive traces are visible. The flexcircuit board contains the 1^(st) stage compensation in the time delaymodel for pair combinations 45-36, 36-12, and 36-78. This is done by theflex circuit board 24 employing pad capacitors to add compensatingcrosstalk having a polarity opposite that of the plug. These padcapacitors are C46 and C35 for pair combination 45-36, C26 for paircombination 36-12, and C37 for pair combination 36-78. Additionally, thecapacitance values of the capacitors are chosen so that the modeconversion across the pairs 45-36, 36-12, and 36-78 is reduced.

Referring to FIGS. 3-5, the flex circuit board has the followingfeatures:

-   -   1) The flex board 24 wraps around the nose 14 such that the top        layer of the flex board makes contact with the PICs (the area        where contact is made is highlighted in FIG. 5).    -   2) Crosstalk compensation with a polarity opposite that of the        plug for pair combination 45-36 is provided by pad capacitors        C35 and C46. The area of each pad capacitor is 0.0323″ by 0.044″        (±20%), and each has a capacitance of approximately 1.2 pF. The        schematic for pair combination 45-36 can be seen in FIG. 13.    -   3) Crosstalk compensation with a polarity opposite that of the        plug for pair combination 36-12 is provided by pad capacitor        C26. The area of this pad capacitor is 0.03″ by 0.033″ (±20%),        and the capacitor has a capacitance of approximately 0.85 pF.        The schematic for pair combination 36-12 can be seen in FIG. 11.    -   4) Crosstalk compensation with a polarity opposite that of the        plug for pair combination 36-78 is provided by pad capacitor        C37. The area of this pad capacitor is 0.03″ by 0.033″ (±20%),        and the capacitor has a capacitance of approximately 0.85 pF.        The schematic for pair combination 36-78 can be seen in FIG. 12.

Rigid Circuit Board 16

The rigid circuit board 16 shown in FIG. 1 is illustrated in more detailin FIGS. 6-8. FIG. 6 shows a schematic view of the rigid circuit board,FIG. 7 shows conductor layouts on different layers of the board, andFIG. 8 is a “see-through” perspective view showing all of the conductivelayers of the board. The rigid circuit board 16 contains the 1^(st) andonly stage of crosstalk compensation for pair combination 45-78. Itcontains both the 1^(st) and 2^(nd) stage of time delay crosstalk forpair combination 45-12. Additionally, it contains the 2^(nd) stage ofcrosstalk in the time delay model for pair combinations 36-12 and 36-78.It also contains the 2^(nd) stage lattice network crosstalk for paircombination 45-36. The method of adding capacitors on the rigid board ischosen so that the mode conversion across all pairs is reduced.

Referring to FIGS. 6-8, one embodiment of the rigid circuit board hasthe following features:

-   -   1) This rigid board design incorporates non-plated holes drilled        into the board (some are highlighted in FIG. 8). These holes are        used to reduce the distributed capacitance between wires 4 and        5; and 3 and 6 by lowering the effective dielectric constant        between respective traces through the addition of air gaps so        that the return loss on these pairs is further improved. This        “variable dielectric” over the length of a trace can be used to        improve performance of the jack.    -   2) Current carrying traces are routed between PIC vias and IDC        vias with the respective pin numbers. PIC vias refer to the vias        where the compliant pins from nose 14 interface with the rigid        circuit board 16, shown in FIG. 1. The IDC vias refer to the        vias where the IDCs 18 interface with the rigid circuit board        16.    -   3) Crosstalk having the opposite polarity of the net crosstalk        caused by the plug for pair combination 45-78 is provided by pad        capacitor C47 connected between the 4 and 7 PIC vias, and by pad        capacitor C58 connected between the 5 and 8 PIC vias. Both of        these capacitors have areas of 0.02″ by 0.02″ (±20%). A        schematic for pair combination 45-78 is shown in FIG. 9.    -   4) Crosstalk compensation for pair combination 45-12 is achieved        by using the time delay model. A schematic for pair combination        45-12 is shown in FIG. 10. Pad capacitor C14 has the opposite        polarity from the net crosstalk caused by the plug for pair        combination 45-12 and connects between PIC vias 1 and 4. Pad        capacitor C15 has the same polarity as the net crosstalk caused        by the plug for pair combination 45-12 and connects between IDC        vias 1 and 5. C15 is time delayed from C14 by approximately        0.395″ (average distance between the 1, 2, 4, and 5 PIC vias to        their respective IDC vias). The area of the pad capacitor C14 is        0.021″ by 0.021″±20%, and the area of the pad capacitor C15 is        0.028″ by 0.028″±20%.    -   5) Crosstalk compensation for pair combination 36-12 is achieved        by a pad capacitor C16 having the same polarity as the net        crosstalk caused by the plug. It is connected between PIC via 1        and IDC via 6. This pad capacitor works in tandem with the pad        capacitor C26 on the flex circuit board using the time delay        method to achieve NEXT performance exceeding 500 MHz for pair        combination 36-12. The area of pad capacitor C16 is 0.035″ by        0.061″ (±20%). The schematic for pair combination 36-12 can be        seen in FIG. 11.    -   6) Crosstalk compensation for pair combination 36-78 is achieved        by a pad capacitor C38 having the same polarity as the net        crosstalk caused by the plug. It is connected between IDC via 3        and IDC via 8. This pad capacitor works in tandem with the pad        capacitor C37 on the flex circuit board using the time delay        method to achieve good NEXT performance at frequencies exceeding        500 MHz for pair combination 36-78. The area of pad capacitor        C38 is 0.01″ by 0.01″ (±20%). The schematic for pair combination        36-78 can be seen in FIG. 12.    -   7) Crosstalk compensation for pair 45-36 is achieved by a        lattice compensation technique. This lattice network includes        the following:        -   a. A pad capacitor C35 having opposite polarity from the net            crosstalk caused by the plug for pair combination 45-36            connected between PIC vias 3 and 5. The pad capacitor area            is 0.013″ by 0.013″ (±20%).        -   b. A capacitor C46 of approximately 0.2 pF having opposite            polarity from the net crosstalk caused by the plug for pair            combination 45-36 which is created by the capacitance            between trace 4 (leading to the C47 capacitor) and PIC via 6            (shown in FIG. 8). A small pad capacitor could be added here            if the process, manufacturing, or engineering designs            require it, but this capacitor's size should remain under            0.02″ by 0.02″.        -   c. A pad capacitor C34 having same polarity of the net            crosstalk caused by the plug for pair combination 45-36 is            connected between wires 3 and 4 utilizing a self-inductive            stub L3 of approximately 0.8″ in length running between PIC            3 and the C34 pad capacitor. The other pad of the C34            capacitor terminates another self-inductive stub L4 of            approximately 0.8″ in length, which leads to a via on            current carrying trace 4. The area of pad capacitor C34 is            0.029″ by 0.029″ (±20%).        -   d. A pad capacitor C56 having the same polarity as the plug            for pair combination 45-36 is connected between conductors 5            and 6 utilizing a self-inductive stub L6 of approximately            1.1″ in length. The self-inductive stub L6 is connected to            PIC 6, and runs to the C56 pad capacitor with time delay.            The other pad of the C56 capacitor is connected to another            self inductive stub L5 of approximately 0.8″ in length,            which runs to a via on current carrying trace 5. The area of            pad capacitor C56 is 0.03″ by 0.03″ (±20%).        -   e. The reason inductive stubs L4 and L5 do not connect            directly to the PIC vias is that this allows for improved            return loss in the jack by adding additional length away            from the PICs.        -   f. The schematic for pair combination 45-36 can be seen in            FIG. 13, which further illustrates the lattice network used            in this design.

Description of Overall Jack Compensation Technique for Each PairCombination

This section describes how the flex board 24 and rigid board 16 worktogether in one embodiment of a jack.

Pair Combination 45-78

The schematic for pair combination 45-78 is shown in FIG. 9. Thecompensation technique on pair combination 45-78 does not use the flexboard for any of its capacitors. It does not use the time delay orlattice network techniques either.

Pair Combination 45-12

The schematic for pair combination 45-12 is shown in FIG. 10. Thecompensation technique on pair combination 45-12 does not use the flexboard for any of its capacitors. It does not use the lattice networkeither. However, it does make use of the time delay method by having C15time delayed by approximately 0.395″ (average distance between the 1, 2,4, and 5 PIC vias to their respective IDC vias) from C14 (with bothcapacitors on rigid board 24).

Pair Combination 36-12

The schematic for pair combination 36-12 is shown in FIG. 11. Itincludes capacitor C26 on flex board 24 and C16 on rigid board 16. C16is time delayed by approximately 0.68″ from the C26. This includes the0.5″ length from the flex board to the PIC rigid board interface, and anadditional length of 0.18″ on the rigid board (based on half thedistance between the 3 and 6 PIC vias and their respective IDC viassince the connection for pair 1 is on the PIC via whereas the connectionfor pair 6 is on the IDC via). There is no lattice network used on paircombination 36-12.

Pair Combination 36-78

The schematic for pair combination 36-78 is shown in FIG. 12. Itincludes capacitor C37 on flex board 24 and capacitor C38 on rigid board16. C38 is time delayed by approximately 0.75″ from C37. This includesthe 0.5″ length from the flex board to the PIC rigid board interface,and an additional length of 0.25″ on the rigid board (based on half thedistance between the 3, 6, 7, and 8 PIC vias and their respective IDCvias). There is no lattice network used on pair combination 36-78.

Pair Combination 45-36

The schematic for pair combination 45-36 is shown in FIG. 13. Itincludes capacitors C35 and C46 on flex board 24. It also includes C35,C46, C34, C56, L3, L4, L5, and L6 on the rigid circuit board 16.Capacitors C34 and C56 are time delayed from the flex circuit boardcapacitors C35 and C46 by approximately 0.56″. This includes the 0.5″length from the flex board to the PIC rigid board vias, and anadditional length of 0.06″ on the rigid board (based on half thedistance between the 4 and 5 PIC vias and the plated through hole viaswhere the stubs associated with conductors 4 and 5 tap off). Thecombination of the capacitors on the flex circuit board 24, thecapacitors on the rigid board 16, and the inductors comprises a latticenetwork. The addition of inductors L3, L4, L5, and L6 with C34 and C56create a frequency-dependent vector that grows at a faster rate withfrequency than the crosstalk caused by the C35 and C46 capacitors. Thisin turn allows for additional bandwidth on 45-36 NEXT up to andexceeding 500 MHz.

Additional Embodiments of Rigid Board 16 Additional Embodiment 1:Adjusting Trace Geometry

This embodiment, which gains additional NEXT bandwidth on paircombination 36-78, is shown in FIG. 14. This embodiment incorporates allaspects of the design described elsewhere herein except for thedifferences highlighted. The main reason for this change in routing isto reduce the parasitic capacitance between contacts 6 and 8 that canoccur with L6. Note that several capacitor sizes are slightly changed toaccount for the new layout but stay within the aforementioned toleranceranges. Also note that a C68 capacitor may be added to the design toallow this rigid circuit board to work with the flex board described inFIGS. 3-5. The schematic for this 36-78 pair combination is similar toFIG. 12, with the exception that the 0.25 pF parasitic capacitance onthe rigid board has been made slightly smaller.

Additional Embodiment 2: Adjusting Trace Geometry and BalancingCapacitance on Pair 45-12

This embodiment, which gains additional NEXT bandwidth on paircombination 36-78, is shown in FIG. 15. This embodiment incorporates allaspects of the design described elsewhere herein, including both themain description and Additional Embodiment 1, except for the differenceshighlighted. The main reason for this change was to improve the modeconversion across pair combination 45-12 by adding C25. Note thatseveral capacitor sizes are slightly changed to account for the newlayout. A schematic for 45-12 is shown in FIG. 16. Note that for thisschematic, C14, C25, C15, and C24 are all closer in their net valueacross the schematic which will result in improved mode conversioncharacteristics.

1. A communication jack for use in a communication network, said jackhaving a plurality of plug interface contacts for making conductivecontact with contacts of a plug, said communication jack comprising:eight current-carrying paths through the communication jack, saidcurrent-carrying paths comprising first, second, third, and fourthdifferential pairs of conductors, each of said differential pairscomprising a first and a second conductive pathway; compensationcircuitry adapted to decrease the overall crosstalk when saidcommunication jack is connected to a plug, said compensation circuitrycomprising: a first pad capacitor connected between the first conductivepathway of the first differential pair and the second conductive pathwayof the second differential pair; a second pad capacitor connectedbetween the second conductive pathway of the first differential pair andthe first conductive pathway of the second differential pair; a thirdpad capacitor connected between the first conductive pathway of thesecond differential pair and the first conductive pathway of the fourthdifferential pair; and a fourth pad capacitor connected between thesecond conductive pathway of the second differential pair and the secondconductive pathway of the third differential pair; wherein said first,second, third, and fourth capacitors are provided on a flexible circuitboard in electrical contact with said plug interface contacts.
 2. Thecommunication jack of claim 1 further comprising a rigid circuit boardcontaining additional compensation circuitry.
 3. The communication jackof claim 1 wherein said plug interface contacts number eight andcorrespond to said eight current-carrying paths through saidcommunication jack.
 4. The communication jack of claim 2 furthercomprising a plurality of insulation displacement contacts connected tosaid rigid circuit board.
 5. The communication jack of claim 1 whereinsaid plug interface contacts wrap around a nose of said jack and whereina top layer of said flexible circuit board makes contact with said pluginterface contacts in the area of said nose.
 6. The communication jackof claim 2 wherein said additional compensation circuitry on said rigidcircuit board comprises crosstalk compensation circuitry forcompensating crosstalk between the first and fourth differential pairs.7. The communication jack of claim 6 wherein said additionalcompensation circuitry on said rigid circuit board further comprisescrosstalk circuitry for compensating crosstalk between the second andthird differential pairs.
 8. The communication jack of claim 7 whereinsaid additional compensation circuitry on said rigid circuit boardfurther comprises crosstalk circuitry for compensating crosstalk betweenthe second and fourth differential pairs.
 9. The communication jack ofclaim 8 wherein said additional compensation circuitry on said rigidcircuit board further comprises second stage lattice network crosstalkbetween the first and second differential pairs.